HISTOLOGICAL STUDIES ON THE PYLORIC STOMACH AND ITS APPENDAGES INOREASTER RETICULATUS(L.) (ASTEROIDEA)

Abstract

This paper presents a detailed histological study of those parts of the digestive system of Oreaster reticulatus lying between the upper limits of the cardiac stomach and the beginning of the intestine. In all parts, the wall of the gut consists of the same tissue layers found in other asteroids studied. Of these layers, the lining epithelium is histologically most diverse, containing the following types of cells: typical cells, most common and least specialized, with brush border and flagellum; zymogen cells, here as in other asteroids filled with secretion granules often associated with a vacuole; mucous gland cells, containing a frothy, vacuolate mass of secretion showing characteristic staining reactions; globule cells, in which the secretion consists of coarse, spherical globules staining in such a way as to suggest that they may represent a mucosubstance different from the product of the mucous gland cells; and basal cells, of unknown significance, often present in crowded masses in the epithelium, containing either a clear vacuole or an accumulation of granular material. All of these types of cells are present in the various digestive organs in characteristic patterns of distribution and combination, and these patterns have been described in detail for Tiedemann's duct and pouches, the glandular pockets and median duct of the pyloric caecum, the radial reservoirs, and the sets of fold-patterns in the roof of the pyloric stomach. It is noted that although some parts of the system, such as Tiedemann's pouches with their parallel wall striations, and the radial reservoirs, may resemble each other superficially in different species, close histological comparison shows important differences. Judging from staining behavior, mucous gland cells appear to be similar in all asteroids that have been studied, including Oreaster, but the properties of the secretion-product of these glands seem to differ from those of related substances produced by any of the several types of mucous gland cells found in the digestive systems of echinoids. The basal cells in Oreaster, are believed to correspond to cyst-like bodies, previously described, occurring in similar locations in the lining of the gut in Patiria but apparently not in other asteroids studied.